Preheat your oven to 350°F (175°C). Grease a 9-inch baking pan with butter or non-stick spray and set aside.
In a large mixing bowl, combine 1 ½ cups flour, ¾ cup sugar, baking powder, and salt. Add the cold, diced butter and use a pastry cutter or your fingertips to work the butter into the dry ingredients until the mixture resembles coarse crumbs with small pea-sized bits.
2 eggs large eggs, 1 teaspoon vanilla extract
Add eggs, milk, and vanilla extract to a separate bowl. Whisk until well combined and set aside. Gradually pour this mixture into the dry ingredients, folding gently with a spatula until just combined. Do not overmix.
2 eggs large eggs, ½ cup milk, 1 teaspoon vanilla extract
Gently fold the fresh blueberries into the batter, distributing evenly without overmixing to prevent the berries from breaking.
1 cup fresh blueberries
Pour the batter into the prepared baking pan, spreading evenly with a spatula. In a small bowl, combine ½ cup brown sugar, ⅓ cup flour, cold diced butter, and cinnamon. Use a fork or your fingers to cut the butter into the dry ingredients until the mixture resembles coarse crumbs for the streusel topping.
½ cup brown sugar, ⅓ cup all-purpose flour, ¼ cup unsalted butter, ½ teaspoon ground cinnamon
Sprinkle the streusel evenly over the batter in the pan. Bake in the preheated oven for approximately 40-45 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
Remove the cake from the oven and allow it to cool in the pan for 10 minutes. Then transfer to a wire rack and cool completely before slicing to observe the moist crumb with a vibrant blueberry swirl and crunchy streusel topping.
